Since the time of its invention in the early 1800's, the stethoscope has been used routinely by physicians to amplify sounds in the human body. The physician typically places the chest piece of the stethoscope against the patient's skin and listens through the stethoscope's earpieces. By monitoring a patient's breathing, a physician may detect the existence of adventitious (i.e., abnormal and/or unexpected) lung sounds. The identification and classification of adventitious lung sounds, moreover, often provides substantial information about pulmonary and associated abnormalities.
Adventitious lung sounds may be classified into two major types: pulmonary and pleural. Pulmonary lung sounds, moreover, may be categorized as crackles (or rales), which are discontinuous (i.e., interrupted) sounds, and wheezes and rhonchi, which are continuous. Crackles may be further classified as coarse, medium or fine, depending on their frequency, characteristics and amplitude. Wheezes may be similarly classified as sibilant or sonorous. An experienced and knowledgeable physician, moreover, may be able to diagnosis certain pulmonary diseases, such as pneumonia, asthma, etc., simply by detecting, identifying and noting the location of particular adventitious sounds.
Lung sounds may also be recorded and displayed to assist in the detection and identification of adventitious sounds. For example, U.S. Pat. No. 3,990,435, entitled BREATH SOUND DIAGNOSTIC APPARATUS to Raymond L. H. Murphy, Jr., the inventor herein, discloses a system for providing a time-expanded visual display of lung sounds. That is, the time scale of the tracing or waveform detected by a microphone, normally plotted at approximately 25-50 mm/sec. by standard medical strip charts, is expanded to approximately 800 mm/sec. Expanding the time scale of the waveform significantly improves the physician's ability to detect and identify adventitious sounds.
Devices to analyze recorded lung sounds are also known. For example, U.S. Pat. No. 5,010,889, entitled INTELLIGENT STETHOSCOPE to Bredesen et al., discloses a stethoscope capable of digitizing and storing body sounds, including heart and lung sounds, in a memory structure configured to store up to six different sounds. The stethoscope includes a single chest piece with a microphone which may be moved to one of six locations around the patient's chest. The stethoscope further includes an LCD panel for displaying the waveform of a recorded sound.
Using waveform signature analysis, each of the six recorded waveforms is examined to determine the presence of high-pitch sounds which may correspond to fine crackles or low-pitch sounds which may correspond to coarse crackles. The presence or absence of these sounds is then formed into an array that may be compared with pre-recorded arrays corresponding to known conditions, e.g., normal lung sounds, pneumonia, etc. If a match is found between the recorded waveforms and one of the pre-recorded arrays, a diagnosis may be displayed on the LCD panel of the stethoscope.
Although Bredesen's intelligent stethoscope represents an improvement in diagnostic tools, especially for physicians lacking extensive experience in detecting and identifying adventitious lung sounds, it nonetheless has several disadvantages. First, the intelligent stethoscope has only a single microphone, so that obtaining recordings at multiple locations is time-consuming. A single microphone also makes it impossible to record a given sound (e.g., a particular inspiration or expiration) from more than one point on the chest. Second, the small LCD panel is capable of displaying only a single waveform in one predefined format and is provided simply to determine whether valid data has been obtained. Due to these limitations, the intelligent stethoscope is not that likely to provide accurate diagnoses.